Choppers are often used with battery-powered electronic flash units to achieve a most effective transformation of the D.C. battery voltage. Primarily, mechanical and transistorized choppers are used for this function. The use of an electronic chopper circuit or converter is particularly advantageous since any maintenance of mechanical contacts is eliminated and a long life span is achieved. The switching frequency for D.C. to D.C. chopper converters can be chosen over a wide range. Transformer size or volume decreases as the switching frequency increases. Based on their operating characteristics, one differentiates between single-ended and double-ended, shunt-series, on the one hand, and push-pull chopper converter configurations, on the other hand. Basically, all such circuits consist of one or two transistors and of oscillation transfer-means. Through the action of these transistors, a D.C. voltage is alternately applied to, and removed from the primary winding of the oscillation transfer means. The resulting alternating voltage has a rectangular waveform and is thereby transformable.
There have been numerous choppers and oscillators proposed which are suitable for alarm systems, fluorescent lamps, high voltage blinkers, radio receivers and flash units. [Siemens - Halbleiter-Schaltbeispiele, Ausgabe April 1962, Seite 21 bis 35; (Siemens Semiconductor Circuit Examples, April 1962 Issue pages 21-35); H. Pitsch, Lehrbuch der Funkemphangstechnik II, 4. Auflage, 1964, Sec. 965, (H. Pitsch, Text of Radio Receiving Technology II, 4th edition 1964, p 965; G. Bender, Das Electronische Fotoblitzgeraete, 2. Auflage 1962, S. 57, (G. Bender, The Electronic Photo Flash Unit, 2nd edition, 1962, p. 57)]. These choppers and oscillators are not optimally usable in electronic flash units since they operate continuously, thus utilizing excess energy.
A circuit configuration which interrupts the charging sequence of the flash capacitor, and thus limits any unnecessary energy consumption, is also known. [F. Eberhard, Ein Netzgeraet fuer Profiblitzgeraete, Funkschau 1975 Heft 5, S. 64-66, (F. Eberhard, A Power Supply for a Professional Flash Unit, Radio Show Volume 5, pgs 64-66)]. This voltage regulation circuit is interrupted upon reaching the desired output or charging voltage of the flash capacitor by shutting off the thyristor controlling the charging current. This circuit is intended for mains-fed power supplies and is therefore not optimally usable for battery-driven flash-unit applications, since even upon turn off of the charging thyristor, energy would still be consumed.